External fixation systems have been known for many decades. Such systems generally include a framework mounted around the bone fracture with a series of pins extending from the framework into the bone. Various forms of such systems are known including a quadrilateral system conventionally practiced with a Vidal frame as well as bilateral systems and unilateral systems. In general these systems promote bone union by stabilizing the position of the bone fragments. For some fracture patterns it is possible to compress the bone segments so as to achieve greater stability and speed union. However, in fractures with extensive comminution or bone loss, the fracture cannot be compressed without limit or shortening will occur.
In an exemplary practice, such frames are used for treating various leg bone fractures. When using rigid external fixation frames the majority of force from muscle pull or ambulation is transmitted through the frame and not the bone. After the healing process has begun, however, with the formation of soft callus between the bone ends, it would be desirable to permit the patient to exert a limited load on the bone and callus so as to encourage a stronger union. Conventional systems, however, either apply only static compression or static neutralization.